Advanced Placement (AP) Chemistry Practice Exam

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What does the symbol ΔS represent in thermodynamics?

Change in enthalpy
Change in entropy
Change in Gibbs free energy
Change in temperature

The correct answer is: Change in entropy

In thermodynamics, the symbol ΔS specifically represents the change in entropy of a system. Entropy is a measure of the disorder or randomness of a system, and ΔS quantifies how that disorder changes as a reaction occurs, or as a physical process takes place. Understanding entropy is crucial because it plays an integral role in the second law of thermodynamics, which states that the total entropy of an isolated system can never decrease over time. In various processes, such as mixing, phase changes, and chemical reactions, a positive change in entropy (ΔS > 0) indicates that the system is moving toward greater disorder, while a negative change (ΔS < 0) indicates a move toward more order. In the context of the other options, change in enthalpy is represented by ΔH, change in Gibbs free energy is shown as ΔG, and change in temperature is denoted by ΔT. Each of these symbols corresponds to different thermodynamic quantities, emphasizing the distinct role that ΔS plays within the framework of thermodynamics.